lactose

lactose

a white crystalline disaccharide occurring in milk and used in the manufacture of pharmaceuticals and baby foods. Formula: C₁₂H₂₂O₁₁

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Lactose

Milk sugar or 4-O-β- d -galactopyranosyl- d -glucose. This reducing disaccharide is obtained as the α- d anomer (see formula, where the asterisk indicates a reducing group); the melting point is 202^°C (396^°F). Lactose is found in the milk of

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mammals to the extent of approximately 2–8%. It is usually prepared from whey, which is obtained by a by-product in the manufacture of cheese. Upon concentration of the whey, crystalline lactose is deposited.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

lactose

[′lak‚tōs]

(biochemistry)

C₁₂H₂₂O₁₁ A disaccharide composed ofD-glucose andD-galactose which occurs in milk. Also known as lactin; milk sugar.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Lactose

 

(milk sugar), C₁₂H₂₂O₁₁, a disaccharide, formed from D-galactose and D-glucose radicals; it exists in the a- and β- forms. Crystalline lactose is obtained in three modifications: α-form (melting point, 223°C), β-form (melting point, 252°C), and the α-form monohydrate (melting point, 202°C). Lactose is soluble in water, diluted ethyl alcohol, and pyridine and insoluble in ether and absolute alcohol; it separates into galactose and glucose during acidic hydrolysis.

Lactose occurs in free form (2–8.5 percent) in the milk of all mammals and is included in the composition of oligosaccharides, glycolipides, and glycoproteins. It has also been found in the pollen tubes of some plants. Lactose biosynthesis is effected by the enzyme galactosyl transferase, which catalyzes the transfer of the galactose radical from uridine diphosphate galactose to D-glucose. The enzymatic hydrolysis of lactose proceeds upon action of β-galactosidase. The absence of galactosidase in the mucous membrane of a newborn’s intestines is a hereditary disease that may lead to death if lactose is not excluded from the diet.

D. M. BELEN’KII

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.